ABSTRACT

Biochar is known to be a highly adsorptive material, especially when the biochar is altered by activation to further increase its sorption ability. Little information, however, is available on the potential reversibility of both ammonium (${\mathrm{NH}}_4^{+}$) and nitrate (${\mathrm{NO}}_3^{-}$) sorption on the inherent biochar pH. The objective of our study was to characterise biochars made using different pyrolysis conditions from five various plant materials and rubber tyre, and to use them to investigate the biochar properties responsible for ${\mathrm{NH}}_4^{+}$ and ${\mathrm{NO}}_3^{-}$ adsorption and desorption. The rubber tyre, maize stover and sugarcane pith were the weakest adsorbing biochars (5.7–7.8 mg g⁻¹) and best described by the Freundlich adsorption isotherm. The grape pip, grape skin and pine wood biochars had adsorption capacities in the range 8.3–9.4 mg ${\mathrm{NH}}_4^{+}$ g⁻¹ and best described by a linear adsorption isotherm at 100 mg L⁻¹. The ${\mathrm{NH}}_4^{+}$ adsorption results were associated with physisorption which implies that they can act as slow release ${\mathrm{NH}}_4^{+}$ fertilisers if ${\mathrm{NH}}_4^{+}$ is bioavailable. The six biochars had ${\mathrm{NO}}_3^{-}$ adsorption capacities in the range 15.2–15.9 mg g⁻¹ and were well fitted to the linear adsorption isotherm at 100 mg L⁻¹. All six biochars had a stronger ${\mathrm{NO}}_3^{-}$ removal affinity (82–89%) compared to ${\mathrm{NH}}_4^{+}$ (33–39%). Adsorbed nitrate was not desorbable (0.01–0.23%) compared to adsorbed ${\mathrm{NH}}_4^{+}$ which was 53–60% desorbable. The desorption result was possibly due to ${\mathrm{NO}}_3^{-}$ competing redox reactions or ${\mathrm{NO}}_3^{-}$ being too strongly adsorbed for extraction. Desorption of ${\mathrm{NH}}_4^{+}$ was associated with biochar net negative pH values and volatilisation of ammonia.

摘要

众所周知，生物炭是一种高吸附性材料，特别是当生物炭通过活化改变以进一步提高其吸附能力时。然而，关于这两种铵的潜在可逆性的信息很少（${\mathrm{NH}}_4^{+}$) 和硝酸盐 (${\mathrm{不}}_3^{-}$) 吸附在固有的生物炭 pH 值上。我们研究的目的是表征使用五种不同植物材料和橡胶轮胎的不同热解条件制成的生物炭，并使用它们来研究负责的生物炭特性${\mathrm{NH}}_4^{+}$和${\mathrm{不}}_3^{-}$吸附和解吸。橡胶轮胎、玉米秸秆和甘蔗髓是最弱的吸附生物炭（5.7-7.8 mg g ^-1），并且最好用 Freundlich 吸附等温线来描述。葡萄籽、葡萄皮和松木生物炭的吸附能力在 8.3-9.4 mg 范围内${\mathrm{NH}}_4^{+}$g ^{-1最好用 100 mg L -1}的线性吸附等温线来描述。这${\mathrm{NH}}_4^{+}$吸附结果与物理吸附有关，这意味着它们可以作为缓慢释放${\mathrm{NH}}_4^{+}$肥料如果${\mathrm{NH}}_4^{+}$是生物可利用的。六个 biochars 有${\mathrm{不}}_3^{-}$吸附容量在 15.2-15.9 mg g ^{-1范围内，很好地拟合了 100 mg L -1}的线性吸附等温线。所有六种生物炭都具有更强的${\mathrm{不}}_3^{-}$去除亲和力 (82–89%) 相比${\mathrm{NH}}_4^{+}$(33–39%)。与吸附的硝酸盐相比，吸附的硝酸盐不可解吸 (0.01–0.23%)${\mathrm{NH}}_4^{+}$这是 53-60% 可解吸的。解吸结果可能是由于${\mathrm{不}}_3^{-}$竞争性氧化还原反应或${\mathrm{不}}_3^{-}$吸附太强而无法萃取。解吸${\mathrm{NH}}_4^{+}$与生物炭净负 pH 值和氨的挥发有关。